1. Field of the Invention
The present invention relates to manually operated reciprocating pumps for dispensing liquids from a container.
2. Background of the Invention
A conventional throttling pump for dispensing liquids from a container includes a hollow body having opening in each end, into the upper end of which is fitted a hollow piston which is slidable reciprocally in the body with sealing fit, which piston is connected at its upper end to an actuator. The piston and body define an interior chamber having an opening at each end. The upper opening of the piston connects with a nozzle of the actuator from which the liquid is dispensed. An outlet valve is located in the upper opening and may be a ball-type valve. An inlet ball-type valve is located in the lower opening in the lower end portion of the body. The ball-type valves comprise floating balls which seat on circular valve seats formed in the piston and body. The operation of such ball-type valves is dependent on liquid pressure causing the ball to move away from the valve seat. Typically, during a dispensing stroke of the piston, force is applied to the actuator, which causes the piston to slide downwardly into the body, causing the piston chamber to decrease in size and the pressure inside the chamber to increase. The liquid pressure inside the chamber causes the upper valve to open, while the lower valve is held closed by the same pressure, so that liquid flows out of the chamber and is dispensed. A spring is provided to return the piston to an up position when the actuator is released. During an upward stroke, a vacuum is formed in the chamber causing the upper valve to close and the lower valve to open so that liquid is drawn through the opening in the lower end of the body into the chamber.
It has been found that the pump described above is prone to leakage around the valves. For example, an increase in temperature can cause the liquid to expand and cause a sufficient pressure increase in the container such that both the upper and lower valves open, allowing the liquid to flow out of container and through the actuator nozzle. Similarly, if the pump is upended there will be leakage around the valves. Accordingly, it is desireable to provide a positive seal for the pump so that a container and pump may be conveniently transported as a unit without having to provide a separate cap for the container which must be replaced by the pump when the unit is to be used.
In addition, it has been found that it is desireable to provide a way for liquid which is in the dispensing nozzle of the actuator to be drawn back into the pump so that drops of liquid are not left on the tip of the nozzle.
An additional problem arises when a conventional pump is used to dispense viscous liquids such as liquid soap or lotions. The conventional pump may be very difficult to prime with such viscous liquids, since the leakage of air around the valves may reduce the vacuum created in the piston chamber by an upward stroke so that there is an insufficient pressure differential between the piston chamber and the container, to overcome gravity and the flow resistance of the viscous liquid.
A final problem associated with the conventional pump design is its reduced effectiveness when it is not vertically oriented during use. Since during the initial portion of the piston stroke, before a pressure differential is developed, the balls of the valves are held in place by gravity, the balls may not seal the valves if the pump is moved from the vertical position. In addition, when a viscous liquid is being pumped, the balls will tend to be suspended in the liquid and the sealing of the valves will be slowed, reducing the pump's effectiveness.
Several improvements over the conventional pump design have been proposed. U.S. Pat. No. 4,606,479 to Van Brocklin discloses a pump in which the ball-type valves of the conventional pump are replaced with a valve member which is movable inside the piston and operates as an upper valve by seating its upper end in a valve seat in the upper end of the piston, and which operates as a lower valve by frictionally engaging a cylindrical sleeve which is movable to seat around a ring formed in the lower end of the body. The pump does not however have the capability to draw material back from the actuator nozzle tip.
Other patents of interest include U.S. Pat. No. 3,237,571 to Corsette; U.S. Pat. No. 3,627,206 to Boris; U.S. Pat. No. 4230,242 to Meshberg; and U.S. Pat. No. 4212,332 to Kutik et al.